Method of building a lugged tread on a heavy duty tire



'B. E. RAGAN Filed Dec. 20, 1966 INVENTOR ORNE E. EAGAN MWMMgWQQ Q M METHOD OF BUILDING A LUGGED 'IREAD ON A HEAVY DUTY TIRE m m Km /Hv TC J E s 2% 2% e E U T B U 5C BKGL KS 2A0 N c TIT c CW XB TOE TO NFS NFC

Sept. 2, 1969 United States Patent 3,464,874 METHOD OF BUILDING A LUGGED TREAD ON A HEAVY DUTY TIRE Bradley E. Ragan, Spruce Pine, N.C., assignor to'Brad Ragan Inc., Spruce Pine, N.C., a corporation of North Carolina Continuation-in-part of abandoned application Ser. No. 569,863, Aug. 3, 1966. This application Dec. 20, 1966, Ser. No. 603,340

Int. Cl. 32% 17/37, 17/02 US. Cl. 156-96 6 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation-in-part of application Ser. No. 569,863, filed Aug. 3, 1966 and entitled Method of Building a Lugged Tire Tread, now abandoned.

The tread designs characteristic of large pneumatic tires used with heavy olf-the-road equipment, such as size 11.00 x 20 and larger earthmover tires, are intended primarily to provide traction and/ or protection against sideslip for the equipment, through the use of a tread including lugs extending is desired predetermined directions relative to the crown of the tire. Heretofore, such lugged treads for heavy-duty tires have been renewed in accordance with conventional methods. In following such methods, the carcass of a heavy-duty tire is first buffed down, then built up with sidewalls and relatively thick crown of uncured rubber, and then positioned in an encircling mold which bears a lugged tread design, to mold the tread design into the crown portion of the tire while simultaneously vulcanizing the uncured rubber. In such recapping, the thick crown of uncured rubber on the carcass is provided by a preform known in the trade as camelback, which is manufactured to size for each tire size being renewed.

Significant problems are presented by this method of building treads for large, heavy-duty tires. With such tire sizes, the molds and other equipment used in conjunction with this method are quite expensive, and a large capital investment is required if many of the wide range of heavyduty tire sizes are to be accommodated. While it is conventional practice to accommodate more than one size or manufacture of off-the-road tire in a single toroidal mold by slightly deforming the carcass during the curing period, thereby increasing the number of types of tires which may be accommodated in a limited number of molds, it has heretofore been recognized that curing a tire while in a deformed condition gives rise to a permanent set thereof in the distorted condition. Additionally, a further difiiculty is that carnelback must be stocked in preforrns of the correct size for use with each of the molds employed and has a limited shelf life, thus requiring investment in a large inventory of perishable goods.

In an effort to avoid the difiiculties and expense involved in providing the necessary supplies and equipment and in following the conventional method for renewing heavy-duty lugged tread tires, it has heretofore been proposed to renew such a tire by relugging. Relugging is a method which involves removing a portion of a worn lug to leave a stub having a smooth surface and then securing a length of uncured rubber lug stock to the stub surface. Such a method obviates the use of a tread mold curing vessel and reduces the quantity of uncured rubber stock which must be used in renewing the tread, but does not entirely avoid the inventory problem and introduces serious difiiculties in obtaining a bond between the cured rubber lug stub and the relugging stock.

Conventionally, uncured rubber such as camelback or relugging stock is secured to the tire carcass being renewed through the use of a thin layer of a soft rubber material known as cushion gum. Cushion gum, while necessary to permit obtaining adhesion of the uncured rubber stock to the cured rubber of the tire carcass at a conveniently low temperature, has substantially less tensile strength than either the tire carcass or the stock, both when in the uncured state for application and after curing of the renewed tire. Thus, the renewal of a tread in ac cordance with a method relying on the use of cushion gum results in an inherent plane of weakness at the join of the cushion gum to the tire carcass. Such a weak join is particularly troublesome in a relugged heavy-duty tire of the type to which the present invention is directed, inasmuch as high stresses are imposed on the lugs and will result in separation of the added lug stock from the original carcass.

With the foregoing deficiencies in mind, it is an object of this invention to provide a method of building a lugged tread on a heavy-duty tire which is particularly valuable in renewing such tires for reuse and through which the necessity of stocking uncured rubber materials in specific sizes and equipping a plant with expensive tire mold equipment is avoided while a stronger and more satisfactory retread is obtained.

A further object of this invention is to provide a method of building a lugged tread for heavy-duty tires wherein base stock and lug stock are extruded and applied to a tire carcass, promoting proper bonding and avoiding deterioration of the stock to be used during storage. Through the extrusion and application of stock, as described more fully hereafter, this method is readily adaptable to the full range of tire sizes and tread configurations used in conjunction with heavy-duty equipment.

A further object of this invention is to provide a renewed heavy-duty tire wherein an extended useful life for the renewed tire is facilitated by the structural characteristics of the renewed tire.

Some of the objects and advantages of the invention having been stated, others will appear as the description proceeds, when taken in connection with the accompanying drawing, in which:

FIGURE 1 is a diagrammatic representation of the steps of the method of this invention;

FIGURE'Z is a perspective view of a tire carcass on which a lugged tread is being built in accordance with this invention;

FIGURE 3 is a section view through the tire of FIG- URE 2, taken substantially along the line 3--3 in that figure;

FIGURE 4 is a perspective view of a length of lug stock in accordance with the present invention;

FIGURE 5 is a view similar to FIGURE 3, taken along the line 5--5 of FIGURE 2; and

FIGURE 6 is a section view through the tire of FIG- URE 2, taken substantially along the line 66 in FIG- URE 5.

Referring now more particularly to the drawing, the building of a lugged tread on a heavy-duty tire in accordance with the method of this invention proceeds step by step generally from left to right and from top to bottom of the diagrammatic representation of FIGURE 1. While FIGURE 1 is intended to briefly represent the successive steps undertaken in practicing the method of this invention, it is believed that a better understanding of the method may be obtained by a description given with reference to a tire, such as the tire indicated g nerally at (FIGURE 2), at one stage in the building thereon of a lugged tread in accordance with the method of this invention.

Conventionally, the tire 10 includes sidewall portions 11, 12 which define the shoulders of the tire and the external crown or tread face of the carcass therebetween (FIGURES 3, 5, 6). The initial step of my method is to form the crown of the tire 10 to have a smooth surface, which preferably is accomplished by buffing to substantially remove worn tread lugs therefrom. Bufiing may be done by mounting the tire 10 on a suitable support 14 (FIGURE 2) for rotation adjacent a bufling wheel 15 driven by a motor 13. Such apparatus is conventional and not critical to practice of my method. It is, however, important that the crown surface be properly prepared for further steps in my method by being clean and free from dirt or grease.

In order to avoid insofar as possible disturbing the characteristics of tire construction initially chosen by the designer of the tire, and thereby contribute to increasing the useful life of the renewed tire, it is preferred that the shoulders and sidewalls of the tire, such as the tire 10, remain unbulfed. This is to be contrasted with the usual practice where a full cap is used which includes both a crown portion and sidewalls.

In order to assure the greatest possible area of contact between the cured rubber of the carcass of the tire 10 and the uncured rubber material applied to build up a tread in accordance with this invention, the prepared surface is subsequently encircled with a portion of a strip of base stock. The base stock is formed by extruding uncured rubber as a flat strip having a width substantially the same as the width of the prepared crown surface of the tire 10 and a thickness substantially less than its width. As herein used, the word rubber is intended to refer to all clastomeric materials suitable for use in the manufacture or renewal of large heavy-duty earthmover tires, whether natural, synthetic, or mixtures thereof. Preferably, a portion having a length substantially the same as the circumference of the crown surface of the tire 10 is promptly thereafter severed from the base stock and positioned to encircle the prepared crown surface of the tire 10 to extend entirely over that crown surface. By suitable application of pressure, the base stock portion is stitched, or temporarily adhered, to the cured rubber carcass of the tire 10 (FIGURE 3).

In extruding uncured rubber to form the base stock used in my method, I prefer to employ an extruder such as that described in United States Patent No. 2,958,098, which permits an operator renewing lugged tires to substitute removable dies and readily extrude stock of the requisite width for the various sizes being processed. Additionally, such extrusion at the point of use permits prompt severance of the portion to be used from the extruded body of base stock and stitching to the crown surface while the severed portion is substantially at its extrusion temperature. The extrusion temperature is in excess of 150 F., usually being approximately 170 F., and stitching substantially at this temperature promotes a more uniform and adhesive bond between the cured and uncured rubber than would be obtained at lower bonding surface temperatures. Due to the higher temperature, the more suitable characteristics of the freshly extruded rubber and the large surface area for bonding, the resulting join is substantially stronger than could be obtained through the use of cushion gum and approaches the strength of a unitary block of one of the joined rubber materials.

While it is preferred to stitch the base stock portion 20 to the cured rubber carcass of the tire 10 while the base stock is near the extrusion temperature, it has been found that the large area of surface contact obtained between the base stock and the carcass permits obtaining a bond therebetween of substantially the same strength even when the base stock has been permitted to cool, provided that certain procedures are followed. In order to obtain a strong bond between relatively cool base stock and a cured rubber carcass, and to avoid introducing a plane of weakness in the renewed tire, the surfaces to be adhered are wiped with rubber solvent and afterward coated with a thin layer of a heavy-duty rubber cement such as Goodyears Nylo-Bond. After the carrier for the cement has evaporated, the base stock band is positioned encircling the carcass and stitched into place.

In order to provide built-up lugs for the tread of the tire 10, uncured rubber is similarly extruded to form lug stock 30 (FIGURE 4), which is of trapezoidal crosssectional configuration and has a thickness of approximately one-half of its major width dimension. Preferably (as shown in FIGURE 6) the cross-sectional configuration of the lug stock 30 is that of an isosceles trapezoid, in order to assure that the spaces between lugs in the tread design are substantially self-cleaning.

After extrusion of the lug stock 30, the stock is cut into a plurality of portions 31, each having a length correlated to a dimension of the crown surface of the tire 10 in accordance with the particular lug design to be used in renewing the tire. Each of the portions of the lug stock 30 is then positioned on the tire 10 in a predetermined direction relative to the crown surface and spaced from adjacent lug stock portions at a predetermined distance in order to provide the desired tread design.

If the lug stock portions 31 are at or near the extrusion temperature when stitched to the base stock portion 20 on the crown surface of the tire 10, the portions may be readily deformed to assume any desired direction across the crown surface of the tire, thus making possible the adaptation of the method of my invention to any tread design chosen for use with a large heavy-duty tire. In this connection, it should be pointed out that the particular tread design illustrated in FIGURE 2 is merely illustrative of one type of tread design with which the method of my invention may be used. In addition to deformability of the lug stock portions 31, prompt severance and stitching of these portions assures bonding of the lug stock to the base stock under the most favorable conditions, as the bond is between two surfaces of freshly extruded uncured rubber. Such a joint, subsequent to curing, has substantially the same strength as the remainder of the lug stock portion, and thus readily withstands the stresses imposed during the use of the relugged tire.

The possibility of deforming the lug stock portions 31 while the same are at or near the extrusion temperature, while permitting accommodation thereof to some particular tread designs, may introduce a difficulty if a power driven stitching device is used. In that event, the stitching device may cause undesirable deformation of the lug stock and result in distortion of the desired tread design. Accordingly, where a tread design not requiring deformation of the lug stock is used and the saving in labor realized from a power driven stitching device is desired, it is preferred to apply the lug stock portions 31 after the same have cooled, following the procedure outlined above for application of the band of base stock. As to this application of lug stock, the adhesive bond is between two bodies of uncured rubber material, and thus is substantially stronger, per unit of surface area, than a bond between cured and uncured rubber.

Subsequent to stitching of the lug stock portions 31 to the base stock 20, the built-up lug tread on the tire 10 is cured by being subjected to suitable temperatures and pressures for a required time, as generally known in the working of rubber materials. Such curing, in accordance with the method of my invention, preferably does not involve the use of a mold vessel and is per formed in an open vessel such as that illustrated and described in United States Patent No. 2,271,855. The time and temperature required are determined by the thickness of the base stock and lug stock portions used. I have found, however, that subjecting a heavy-duty tire of the type with which this invention is concerned to a temperature of 260 F. for a period of six to ten hours is satisfactory.

It is believed that curing the built-up lug tread on the tire in accordance with the method of this invention, in an open steam vessel, provides particular advantages and results in increased tread life for the renewed tire. When cured in an open steam vessel, a temperature of approximately 260 is applied to the renewal tread both outwardly from within the carcass and inwardly from the tread surface. This is to be contrasted with conventional mold curing practice wherein a temperature of approximately 295 F. is applied only inwardly from the tread face. In following this conventional practice, the attainment of curing temperatures at the mating surfaces of cured and uncured rubber requires that the tire be maintained at a higher temperature for a substantially longer period of time, and frequently results in overcuring of the wear surface of the tread. A tire cured in accordance with the method of this invention, in an open steam vessel, is satisfactorily cured while being maintained at a lower temperature for a shorter period of time, so that the tread surface retains a greater resilience, to which an increase in useful life is attributed. Additionally, the use of an open steam vessel permits the tire with built-up lugged tread to be cured without distortion, in that the tire may be in a substantially relaxed condition as compared with the deformation heretofore sometimes necessary to force a tire into a mold for curing.

It is apparent that the method herein described makes possible the renewal of large, heavy-duty lugged tread tires, of the type used by earth moving equipment, with a substantial saving in capital investment required while obtaining additional benefits of strengthened wear surfaces and avoidance of distortions in the tire construction. These benefits and advantages are obtained through the use of base and lug stock materials extruded for use with a variety of sizes and tread configurations of tires, applied so as to attain secure bonding, and cured in a manner to avoid the introduction of distortion and maintain a higher degree of resilience than has heretofore conventionally been obtained.

In the drawing and specification, there have been set forth preferred embodiments of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims.

I claim:

1. A method of renewing a heavy-duty tire by building a lugged tread thereon comprising forming a smooth surface encircling the tread face of a tire carcass, extruding a strip of hot rubber base stock having a generally rectangular cross-sectional configuration and a width substantially equal to the width of the smooth surface and substantially greater than the thickness of the strip, then severing from the base stock a portion having a length substantially equal to the circumference of the smooth surface and stitching the base stock portion to the smooth surface,

extruding a strip of hot rubber lug stock having a generally trapezoidal cross-sectional configuration and a major width approximately twice as great as the thickness thereof, and then severing from the lug stock a plurality of portions each having a predetermined length correlated to a dimension of the smooth surface and successively positioning each lug stock portion to extend in a predetermined direction relative to the base stock portion and in a predetermined spaced relation to an adjacent lug portion while stitching the lug stock portion to the base stock portion.

2. A method according to claim 1 wherein the temperature of the base stock portion as the same is stitched to the smooth surface is substantially the same as the extrusion temperature thereof.

3. A method according to claim 2 wherein the extrusion temperature of said base stock is in excess of F.

4. A method according to claim 2 wherein the lug stock portions are cooled following the extrusion thereof and prior to stitching thereof to the base stock portion and further comprising cleaning mating surfaces of the lug stock and base stock portions and applying a thin layer of rubber cement thereto prior to positioning and stitching the lug stock portions.

5. A method according to claim 4 further comprising curing the tire including the build-up lugged tread thereon by uniformly heating the tire within an open steam pressure vessel.

6. A method according to claim 5 wherein the forming of a smooth surface comprises the bufiing of the tire carcass to substantially remove worn tread lugs therefrom; the cross-sectional configuration of the lug stock is that of an isosceles trapezoid; and the lug stock portions are positioned to extend generally transversely of the tread face of the tire.

References Cited UNITED STATES PATENTS 2,611,411 9/1952 Rawls 156-95 X 3,236,709 2/ 1966 Carver 156-96 3,251,722 5/1966 Holman 156-96 X 3,264,162 8/ 1966 Holman 15 6-96 X HAROLD ANSHER, Primary Examiner C. B. COSBY, Assistant Examiner US. Cl. X.R. 

